Information storage and retrieval systems are used to store information provided by one or more host computer systems. Such information storage and retrieval systems receive requests to write information to one or more information storage devices, and requests to retrieve information from those one or more information storage devices.
Certain information storage and retrieval system include two or more clusters, where each cluster includes one or more processors, one or more data caches, and one or more non-volatile storage devices. Upon receipt of a write request, the system writes information received from a host computer to a local data cache, i.e. a data cache disposed in the receiving cluster, and to a “remote” non-volatile storage device, i.e. an NVS disposed in a different cluster.
In the event one cluster fails, the information recently received by that cluster can still be accessed from the remote NVS. In the event both clusters fail in a two cluster system, however, the information written to both caches and both NVSs becomes unavailable. What is needed is a method to rebuild and copy an NVS image in the event, for example, both clusters lose utility power.
Applicants' apparatus provides backup power to each local processor and cache for a limited period of time. During this backup power time interval, Applicants' method rebuilds the remote NVS image using information previously written to the local cache. That virtual NVS image along with the local NVS image is then downloaded to an external storage device for later use.